The tools are usually mounted in a machine which has a rotary cutter wheel from the circumference of which the tools project, or in a chain drag device which carries the points of the tools into contact with the rock or coal. An example of a tool of this general type is found in the disclosure of the U.S. Patent to Krekeler, U.S. Pat. No. 3,331,637, dated July 18, 1967.
Since these tools wear very rapidly, it is important that it be possible to change them readily. They are subject to heavy percussion in their use and any retainer must be such that it will stand up to the rugged conditions. It is also important from the point of view of tool life that the tools be mounted to rotate in the retaining socket. This results in more even wear of the cutting points and insures a longer tool life.
Since the tools are operating in heavy abrasive dust, it is also important that any retaining device be such that it will not become impacted to prevent removal and it should be such that dust will not destroy its effectiveness.
Many retaining devices have been used for mining tools in the form of spring clips, cross pins driven in to a transverse hole, rubber mounted retainers and so forth. Most of these retainers have been mounted on the socket of a tool although some circular retainer rings have been carried in a groove in the end of a tool shank.
The search for a better retainer has, however, continued in an effort to find a device which would provide a better solution to the various problems which arise in use.
The present invention is directed to a structure which is relatively simple, once disclosed, but which has eluded the designers of mining tools even though it was right in front of them in the fastening art. One can surmise that designers have assumed or concluded that the device to be disclosed would not work. However, the inventor of the present structure to be disclosed has jumped the hurdle of conventional thought and has devised a retainer in the form of a double ball spring pressed device which provides many advantages.
The invention permits quick removal and insertion and thus reduces expensive set-up time. The bit and retainer are self-contained so that an inventory of separate retainer parts need not be retained. The device allows free rotation of the bit in the holding block or collet and is clear at the back so dust and cuttings cannot pack in around the back side of the tool. The device is also inexpensive to manufacture and any replacement of worn parts can be readily accomplished when necessary.
The bit has also produced some startling results in the field testing. In addition to the above advantages, it has almost doubled the tool life, thus providing a great savings to the user not only in bit cost but in reduction of down time.